Ignition control



w. F. POTTS IGNITION CONTROL May 5, 1970 Filed Jan. 29, 1968- 2 Sheets-Sheet 1 FIGZ INVENTOR. WILLIAM F. POTTS. BY W -ATIO R NEY May 5, 1970 w. F, POTTS IGNITION CONTROL 2 sheets shee t 2 Filed Jan. 29, 1968 INVENTOR. WILLIAM F, POTTS w 0E Ow ATTORNEY United States Patent 3,510,236 IGNITION CONTROL William F. Potts, Liverpool, N.Y., assignor to Liberty Combustion Corporation, Syracuse, N.Y., a corporation of New York Filed Jan. 29, 1968, Ser. No. 701,191 Int. Cl. F23n 5/20 US. Cl. 431-29 11 Claims ABSTRACT OF THE DISCLOSURE Fluid fuel heating control and ignition system having a burner, an electric fuel valve, an alternating current supply, a pair of electrodes forming a fixed spark gap for the burner, an ignition control circuit connected to the power supply, the valve and electrodes and comprising a spark voltage generator with a transformer, the secondary winding of which provides a high voltage of an oscillatory nature consisting of a series of essentially single cycle pulses, one terminal of the secondary winding being connected to one electrode of the pair of electrodes, the other winding terminal being connected to a common ground line, the generator being operative when energized by said source of power, spark occurrence detection means connected between the other electrode and ground, and having an output point whereat a positive pulse of voltage appears relative to common ground each time a spark discharge occurs in the spark gap and no pulse appears if a spark discharge fails to occur in the gap, valve energizing means operatively connected to the power supply, the valve, and the output point of the spark detection means whereby the valve is energized to open only when spark discharges occur at the spark gap, the energizing means energizing the valve each time a spark discharge occurs for a period of time in excess of the normal period between successive spark discharges.

This invention relates to ignition controls for gas burners predominantly of the solid state type, having fail safe characteristics.

More particularly the invention has to do with solid state circuitry in burner controls, combined with a relay or relays at critical points to provide fail safe operation. Thus the long life characteristics of solid state circuitry, with its low cost, is combined with a relay or relays to provide a low cost circuit, the life expectancy of which is dependent upon the life expectancy of the relay or relays employed and in which fail safe operation is provided for.

In the heating industry, it is vital that ignition controls have both fail-safe characteristics and long-term life expectancy. Nevertheless, it is essential for the success of a product that its cost be as low as possible. The invention, through the use of both semiconductors and electrical relays provides a lost cost ignition control' for gas burners having both fail-safe characteristics and life expectancy limited primarily by the life expectancy of the relays.

The above and other novel features of the invention will appear more fully hereinafter from the following detailed description when taken in conjunction with the accompanying drawings. It is expressly understood that the drawings are employed for purposes of illustration only and are not designed as a definition of the limits of the invention, reference being had for this purpose to the appended claims.

In the drawings, wherein like reference characters indicate like parts:

FIG. 1 is a partial schematic diagram of a preferred means of proving conclusively that a spark is occurring at ice a defined spark gap and that the spark has a minimum amount of energy.

FIG. 2 is a partial schematic of a preferred means of obtaining a useful signal indicating the presence or absence of flame surrounding a defined spark gap used in conjunction with the means for proving the presence and minimum energy of a spark at the same spark gap.

FIG. 3 is a partly schematic and partly block diagram of a gas burner ignition control system incorporating means for both spark and flame proving including means using the latter to cut off the fuel supply in the event of loss of flame or failure to ignite the burner within a predetermined period of time.

FIG. 4 is a block and schematic diagram incorporating in addition to spark and flame proving, a first timing means to delay ignition for a first pre-determined time when the control is first energized and a second timing means for preventing the re-energization of the control for a second pre-determined time after it has been deenergized.

With reference to the following descriptions of the spark proving means and the flame proving means, both of the arrangements to he described are dependent on the use of a spark voltage generator of the capacitive discharge type which provides an output of discrete voltage pulses of high energy but very short duration of the order of a few microseconds and, being oscillatory in nature, each pulse consists essentially of a single cycle of output voltage.

With particular reference to FIG. 1, spark voltage generator 20 is connected to a source of alternating current power via terminals 22 and 24. The output voltage 27 obtained across the secondary 26 of the high voltage transformer in generator 20 is connected directly to first electrode 2.8 of a spark gap and to a common ground line 30*. The second electrode 32 is connected via the cathode and anode of diode rectifier 34 to line 30, diode 34 'being in parallel with capacitor 36. Electrode 32 is also connected through gas discharge tube 38 and resistor 40' to ground line 30 and output voltage 41 is obtained across resistor 40. In operation, output voltage 27 having both positive and negative excursions, for a single cycle, will cause a spark to jump the gap formed between electrodes 28 and 32 and current will flow across the gap, the negative excursion current flowing through diode 34 and the positive excursion current charging capacitor 36 so that the junction of capacitor 36 and gas tube 38 is positive with respect to common line 30.

Since the charge on capacitor 36 will be a function of the energy supplied to it and its capacitance, capacitor 36 must be chosen so that the spark having sufiicient energy to ignite a gas fuel in the gap, will charge capacitor 36 sufficiently to fire gas tube 38 into conduction thereby producing a positive pulse of voltage 41 across resistor 40. In this fashion a positive pulse of voltage 41 is produced for each spark produced by spark generator 20, thus providing a useful signal indicating the presence of a spark in the gap formed .by electrodes 28 and 32. If capacitor 36 is made too large, the charge on it will never reach the firing point of gas tube 38 and so there will be no output signal and if capacitor 36 is made too small the pulse of spark current is too brief to trigger gas tube 38 and again no output pulse will occur.

Thus by the proper choice of capacitor 36 if electrodes 28 and 32 are shorted together so that a spark does not occur the charge on capacitor 36 is discharged back through winding 26 in spark generator 20 so that the charge on capacitor 36 never reaches the firing point of gas tube 38 and again no output pulses will occur. In addition, if either electrode 28 or electrode 32 is grounded to common line 30, no charge will be built up on capacitor 36 and again no output pulse will occur. Furthermore, should diode 34 either be shorted or open circuited the charge on 36 will not reach the firing point of gas tube 38 and output pulses will not occur. In this fashion then, a useful but very simple means is provided for proving the presence of a spark at a defined spark gap when the source of spark voltage is a discrete oscillatory single cycle pulse.

With specific reference to FIG. 2, spark voltage generator 20 is connected to an alternating current source of supply via terminals 22 and 24 and output winding 26 of generator 20 provides a sparking voltage 27 which is of an oscillatory single cycle nature of sufficient magnitude to cause a spark to occur between electrodes 28 and 32. Electrode 28 is connected to one end of winding 26.

The other end of the winding is connected via flame detector circuit 50 to ground common line 30 and electrode 29 being connected to common line .32 via previously described spark detection circuit 44. Flame detector circuit 50 consists of a rectifier diode 54 in parallel with capacitor 56 and in parallel 'with the series arrange: ment of gas tube 58 and resistor 60 as shown in FIG. 2. It is arranged so that when common line 30 is positive with respect to electrode 28, a charge will build up on capacitor 56 sufficient to cause gas tube 58 to fire thereby producing a negative output pulse of voltage 61 across resistor 60 each time that a spark occurs. Diode 54 maintains the integrity of spark detector 44 to detect a short circuit between electrodes 28 and 32. As previously described, the charge on a capacitor is proportional to the energy supplied to the capacitor and the value of the capacitance. Thus capacitor 56 must be chosen with a sufficiently small value of capacitance so that it will charge to the firing point of gas tube 58 each time that a spark occurs between electrodes 28 and 32. It has been proven through repeated experiments that if electrodes 28 and 32 are not enveloped in a flame, capacitor 56 will charge to the firing point of gas tube 58 thereby providing a negative output pulse of voltage '61 each time a spark occurs.

However, if electrodes 28 and 32 are enveloped in a flame, the conductivity of the spark gap in the fla-me will prevent capacitor 56 from reaching a charge sutficient to fire gas tube 58 and no output pulses of voltage 61 will occur across resistor 60. Thus, in the absence of flame at the spark gap, the flame detector 50 will provide a negative output pulse of voltage 61 for each spark occurrence and in the presence of flame enveloping the spark gap, no output voltage pulses 61 will occur. Thus flame detector 30 provides a useful signal indicating the presence or absence of flame enveloping the spark gap.

In FIG. 3, there is shown a schematic diagram of a complete fuel burner system in which electrodes 28 and 32 define a spark gap, the electrodes being fixed in rela tionship to a burner (not shown) whereby fuel issuing from the burner will not fail to be ignited by a spark occurring in spark gap, fuel to the burner being controlled by the energization of winding 66 of a fuel supply valve (not shown), Alternating current power is supplied to this system via terminals 22 and 24, the latter being grounded. The additional elements of the system are spark voltage generator 120 providing oscillatory single cycle output pulses at regular intervals, spark detector circuit 44, valve energizing circuit 68, flame detector circuit 50 and lock-out circuit 80.

In operation, when power is supplied to the system via terminals 22 and 24, spark generator 120 produces output voltage pulses which cause a spark to occur at gap G, the spark being detected by spark detector circuit 44 which triggers valve energizing circuit 68 thereby energizing winding 66 of the fuel valve and allowing fuel to issue at the burner, the fuel being ignited by the spark occurring at gap G. Should the burner fail to ignite before the end of a pre-determined period of time, lock-out circuit 80 will cause spark generator 120 to stop functioning and as a consequence thereof sparks will not occur at gap G. The absence of sparks will be detected by spark detector 44 which will then cause valve energizing circuit 68 to de-energize winding 66 thereby closing the valve and cutting oif the supply of fuel to the burner. Further, during a burning cycle, should the flame at the burner be extinguished for any reason, the absence of the flame will be detected by flame detector 50 and if flame is not reestablished within the pre-determined period of time, lock-out circuit will cause spark generator 120 to stop functioning and the fuel supply will be cut ofl. In either case, lock-out circuit 80 maintains lockout operation until the power supply to terminals 22 and 24 is interrupted momentarily.

In spark generator 120, which is a capacitive discharge type of spark voltage generator, power applied to terminals 22 and 24 will cause capacitor 72 to charge to the peak of the line voltage through resistor 74 and rectifier diode 76 and the primary winding of transformer 25. At the same time, capacitor 81 begins to charge through resistor 82 and diode 83, and eventually the charge on capacitor 81 will reach the firing point of gas discharge tube 84 causing it to conduct, thereby triggering the gate of silicon controlled rectifier 86 and causing rectifier 86 to be conductive. Resistor 88 between the cathode and gate of rectifier 86 prevents transient voltage from triggering rectifier 86 into conduction. When rectifier 86 is triggered into conduction it discharges capacitor 72 through the primary winding of step-up pulse transformer 25 thereby causing a very high voltage to be induced in the secondary of transformer 25 suflicient to cause a spark to occur at gap G. Sparks reoccur at a rate determined primarily by the time constant of resistor 82 and capacitor 81.

As previously described, spark detector circuit 44 provides a positive output pulse across resistors 40 each time that a spark occurs. The gate of silicon controlled rectifier '92 is connected to the junction of gas discharge tube 38 and resistor 40, the cathode of rectifier 62 being connected to the ground line 30, so that each pulse of voltage appearing across resistor 40 will trigger rectifier 92 into conduction. The circuitry of spark generator 120 is arranged so that a spark may occur only when the line connected to terminal 22 is positive with respect to ground so that when rectifier 92 is triggered into conduction it will be able to draw current because the line connected to terminal 22 is positive. When rectifier 92 conducts, it charges capacitor 96 to the peak of the voltage applied to terminals 22 and 24 and this charge is suflicient to cause relay 98 to draw suflicient current through resistor 100 to pull-in, thereby closing relay contact 102 and supplying alternating current power to valve winding 66. Relay 98 is a direct current operated relay having a nominal voltage considerably lower than that of the source of alternating current power and having a very low dropout voltage, so that the charge on capacitor 96 will cause relay 98 to hold in for a time in excess of the period between successive sparks. In the event that rectifier 92 develops an internal short, the charge on capacitor 96 alternates with the AC power supply and consequently relay 98 will not pull-in, and the valve will not open.

In the absence of flame enveloping the spark gap G, flame detector circuit 50 will produce an output voltage at the junction of gas discharge tube 58 and resistor 60, such voltage being a series of negative pulses, one for each spark discharge. The junction of tube 58 and resistor 60 is connected directly to the base of NPN transistor 108 in lock-out circuit 80, the emitter of transistor 108 being connected to the common ground line 30, and its collector being connected through resistor 110 to the junction of diode 76 and capacitor 72 in spark generator circuit 120, the base being also connected through resistor 112 to the junction of resistor 110 and capacitor 72, whereby the charge on capacitor 72 provides a source of direct current supplying base current through resistor 112 and collector current through resistor 110, thereby keeping transistor 108 in a state of saturation. Resistor 114 in combination with resistor 110 provides a voltage divider so that the maximum rating of transistor 108 will not be exceeded.

The negative pulses fed from flame detector circuit will, each time a pulse occurs, cause transistor 108 to cut off for the duration of the pulse thereby allowing capacitor 116 to draw current through diode 118 and resistor 110 from capacitor 72, thus charging capacitor 116 slightly each time transistor 108 is off. The junction of capacitor 116 and diode 118 is connected in turn to one terminal of multilayer diode 119 and through resistor 122 to the common ground line, the other terminal of diode 119 being connected to the gate of silicon controlled rectifier 124. Rectifier 126 connected between the gate and cathode of rectifier 124 acts as a loading resistance to prevent transient voltages from triggering rectifier 124 into conduction. Thus, rectifier 124 will not be triggered into conduction until the charge on capacitor 116 reaches the breakdown voltage of multilayer diode 119 and a finite period of time is required to charge capacitor 116 to this value since the negative pulses from flame detector 50 are very short in duration and consequently allow capacitor 116 to charge only slightly during the brief period that transistor 108 is cut off. Diode 118 is used to prevent these successive charges from discharging back through resistor 114 to the common ground.

The time taken to charge capacitor 116 to the breakdown point of diode 119 is determined primarily by the value of capacitor 116 and resistors 110 and 122. In the continued absence of flame at gap G, rectifier 124 will, after a predetermined time, be triggered into conduction and when this occurs it draws current from the junction of diode 76 and capacitor 72 through resistor 128, this current being of suflicient magnitude to keep rectifier 124 in conduction until the source of alternating current power is removed and the charge on capacitor 72 is dissipated. When rectifier 124 conducts, it draws current also through resistor 82 in spark generator through diode 130 thereby preventing the charge on capacitor 81 from reaching the firing point of gas tube 84 and thereby assuring that rectifier 86 cannot be triggered into conduction and thus stopping spark generator 120 from functioning and cutting off spark voltage to ga-p G. In this fashion, the continued absence of flame at gap G will cause lock-out circuit 80 to cut off the supply of sparks until such time as rectifier 124 is rendered non-conductive by disconnecting the source of alternating current power to the system. In lock-out circuit 80, resistor 122 serves to slowly discharge capacitor 116 when flame is present at gap G, so that the lock-out timing period will not be fore-shortened by any previously acquired charge on capacitor 116'. During the period of flame at gap G transistor 108 remains saturated so that capacitor 116 cannot charge.

FIG. 4 is a schematic diagram of a gas burner igniter control circuit having, in addition to spark sensing and flame sensing and lock-out, a pre-purging timer and postpurging timer to provide a delay for a predetermined period of time when alternating current power is first applied to the system to prevent sparking until the end of this period, and further, when power is disconnected from the system to provide, a second predetermined delay during which the system is prevented from being re-energized.

A set of electrodes 28 and 32 forming a spark gap G are located in fixed relationship to a burner (not shown) whereby a spark occurring in gap G will not fail to ignite fuel issuing from the burner. The winding 66 of an electrically operated valve (not shown) controls the supply of fuel to the burner, an alternating current source of power being supplied to the system via terminals 22 and 2-4, the latter being grounded and connected to a common ground line 30. When power is first applied to the system via terminals 22 and 24, pre-purge timing circuit 132 is energized via normally closed contact 134 of heater relay 136 and begins the purge timing function. At this time power is not supplied to the spark generator 120 nor to the valve energizing circuit 68 because contacts 142 of relay 144 in timing circuit 132 are normally open and relay 144 has not yet been energized.

The pre-purge timing function is performed by a unijunction transistor timing circuit comprising resistor 146, capacitor 148, unijunction transistor 150, resistor 152 and resistor 154, the latter being employed to develop an output pulse of the timer circuit. DC power is supplied to the timing circuit by diode 156 and filter capacitor 158 and the voltage divider comprising resistors 160 and 162. Alternating current is applied to the pre-purge timer only during the timing period via normally closed contacts 164 of relay 144. At the end of the pre-purge timing determined by resistor 146 and capacitor 148, a positive pulse of voltage appears across resistor 154 to trigger SCR 66 into conduction, thereby charging capacitor 168 to the peak of the applied voltage, and providing suflicient current through resistor 170 to energize and pull-in relay 144. Thus contact 142 closes and contact 164 opens. Resistor 170 and capacitor 168 provide a delay to hold relay 144 in the energized position for a short period of time. When contact 164 opens, the prepurge timing circuit is disconnected from the source of alternating power and when contact 142 closes, capacitor 168 continues to be charged on each half cycle of the alternating current power through diode 172 thereby keeping relay 144 energized throughout the balance of the heating cycle.

Concurrent with the closing of contact 142, power is applied to spark generator 120 with the result that sparks will appear across gap G to be detected by spark detector 44, in turn causing valve energizing circuit 68 to energize coil 66 of the fuel valve thereby allowing the valve to open and fuel to issue at the burner as previously described. In this arrangement however, heater relay 136 is in the current path of winding 66 and begins to heat as soon as winding "66 is energized, and after a period of time causes relay contacts 134 to open and remain open so long as heater relay 136 continues to be heated. Since the opening of contact 134 would disconnect the source of power to the system, it is necessary to include a normally-open contact 176 of relay 98 in the valve energizing circuit 68 so that before contact 134 opens, contact 176 is closed thereby assuring the continuation of the supply of power to the system for the heating cycle.

Following the pre-purge period, the absence of flame will be detected by flame detector 50 and lock-out circuit 80 will, after its .pre-determined period, cause spark generator 120 to cease operating. In consequence, relay 98 in the valve actuation circuit 68 Will be de-energized thereby opening contacts 176, cutting off the supply of power to valve winding 66 and to heater relay 136. Heater relay 136 however takes a definite period of time to cool down so that contacts 134 will remain open. Similarly, during a successful burning period when power is disconnected from terminals 22 and 24, relay 98 in the valve circuit 68 will be de-energized and contact 176 will open and, because of the cooling period of heater relay 136, contacts 134 also will remain open for a period of time and in this manner, heater relay 136 prevents re-energization of the system for a period of time after power is disconnected from the system. As will be readily apparent from FIGURE 4 and the foregoing explanation, either the pre-purge timer or the post-purge timer may be used with this system either singly or together. This arrangement provides flexibility for various burner requirements for purging.

While the invention has been progressively illustrated and described diagrammatically, it is to be understood that the invention is not limited to the precise circuitry.

As various changes may be made without departing from the spirit of the invention, as will be apparent to those skilled in the art, reference will be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. For the ignition and control of a fluid fuel heating system having a fluid fuel burner, a supply of fuel controlled by an electrically actuated valve, a source of alternating current power, a pair of electrodes held in fixed relation to each other forming a fixed spark gap therebetween and positioned in fixed relation to said burner whereby fuel issuing from the burner will not fail to be ignited by spark discharges occurring in said gap, an ignition control circuit having means for extending connections to said source of power, said electrical valve and said pair of electrodes comprising a spark voltage generator having an output transformer, the secondary winding of which provides a high voltage of an oscillatory nature, said voltage consisting of a series of essentially single cycle pulses, one terminal of said secondary winding being connected to one electrode of said pair of electrodes, the other winding terminal being connected to a common ground line, said generator being operative when energized by said source of power, spark occurrence detection means connected between the other electrode of said pair of electrodes and common ground, and having an output point whereat a positive pulse of voltage appears relative to common ground each time a spark discharge occurs in said spark gap and no pulse appears if a spark discharge fails to occur in said gap, valve energizing means operatively connected to said source of power, to said electrical valve, and to said output point of said first named means whereby said valve is energized to open only when spark discharges occur at said spark gap, said energizing means energizing the valve each time a spark discharge occurs for a period of time in excess of the normal period between successive spark discharges.

2. An ignition control circuit in accordance with claim 1 wherein the control circuit includes a pre-purge time delay circuit whereby said ignition control circuit is pre vented from operating for a predetermined period of time when the source of power is applied to said ignition control circuit.

3. An ignition control circuit in accordance with claim 1 wherein the control circuit includes a post purge delay circuit connected to be energized while the electrical valve is energized and adapted to prevent said ignition control circuit from being re-energized for a predetermined period of time after said source of power is interrupted.

4. For the ignition and control of a fluid fuel heating system having a fluid fuel burner, a supply of fuel controlled by an electrically actuated valve, a source of alternating current power, a pair of electrodes held in fixed relation to each other forming therebetween a fixed spark gap and positioned in fixed relation to said burner whereby fuel issuing from the burner will not fail to be ignited by spark discharges occurring in said spark gap, an ignition control circuit having means for extending connections to said source of power, said electrical valve and said pair of electrodes comprising a spark voltage generator having an output transformer, the secondary winding of which provides a high voltage of an oscillatory nature, said voltage consisting of a series of essentially single cycle pulses, one terminal of said secondary winding being connected to one electrode of said pair of electrodes, said generator being operative when energized by said source of power, spark occurrence detection means connected between the other electrode of said pair of electrodes and common ground, and having an output point whereat a positive pulse of voltage appears, relative to common ground, each time a spark discharge occurs in said spark gap, and no pulse appears if a spark discharge fails to occur in said gap, valve energizing means operatively connected to said source of power, to said electrical valve and to said output point of said first named means whereby said valve is energized to open only when spark discharges occur at said spark gap, said energizing means energizing the valve each time a spark discharge occurs for a period of time in excess of the normal period between successive spark discharges, flame detecting means detecting the absence of flame conductively enveloping said spark gap, connected between the other secondary terminal of said output transformer and common ground and having an output point whereat a negative pulse of voltage appears, relative to common ground, each time a spark discharge occurs in said spark gap in the absence of flame enveloping said gap, and no pulse appears on the occurrence of a spark discharge when flame is enveloping said gap, and time delay and disabling means operatively connected to said spark generator, said output point of said third named means and common ground whereby said spark generator is disabled upon the continued absence of flame enveloping said electrodes after a predetermined period of time, said dis-' abling continuing until said power source is momentarily interrupted.

5. An ignition control circuit in accordance with claim 4 wherein the control circuit includes a pre-purge time delay circuit operatively connected to prevent said ignition control circuit from operating for a predetermined period of time when the source of power is applied to said ignition control circuit.

6. An ignition control circuit in accordance with claim 4 wherein the control circuit includes a post purge delay circuit operatively connected to prevent said ignition control circuit from operating for a predetermined period of time after said source of power is interrupted.

7. In an ignition control circuit having a spark voltage generator whose output voltage is produced in the secondary winding of a step up transformer having two output terminations one of which is connected through a conducting path to a common ground, said output voltage being oscillatory in nature and consisting of a series of essentially single cycle pulses; a pair of electrodes defining a spark discharge gap therebetween, one electrode connected to the other termination of said transformer and the other electrode connected to ground through a spark occurrence detector consisting of the parallel arrangement of a rectifier diode and a capacitor, the anode of said diode connected to common ground and the cathode to said other electrode and to one terminal of a Voltage breakdown device, the other terminal of said device being connected through a resistor to common ground whereby a positive pulse of voltage occurs across said resistor only when a spark discharge occurs in said spark gap.

8. In an ignition control circuit according to claim 7 wherein the voltage breakdown device comprises a gas discharge tube.

9. In an ignition control circuit having a spark voltage generator whose output voltage is produced in the sec ondary winding of a step-up transformer having two output terminals said output voltage being oscillatory in nature and consisting of a series of essentially single cycle pulses, a pair of electrodes defining therebetween a spark discharge gap, one electrode connected to one terminal of said spark generator, the other electrode connected through a conducting path to common ground, the other terminal of said spark generator being connected to common ground through a flame detector consisting of the parallel arrangement of a rectifier diode and a capacitor, the cathode of said diode connected to common ground and the anode to said other terminal and to one terminal of a gas discharge tube or other voltage breakdown device, the other terminal of said discharge device being connected through a resistor to common ground whereby a negative pulse of voltage occurs across said resistor when a. spark discharge occurs in said spark gap when said electrodes are not conductively enveloped by flame and no negative pulse occurs when said electrodes are conductively enveloped by flame.

' 10. For use in conjunction with a spark voltage gener ator having a pulsed output controlled by the charging of a capacitor through a resistor to a predetermined level, and a source of negative pulses indicating the occurrence of spark discharges in a spark gap defined by a pair of electrodes operatively connected to said spark generator, said negative pulses occurring only when said spark gap is not conductively enveloped in flame, a time delay and disabling circuit comprising of a source of direct current, said DC source connected through a first resistor and the base and emitter of an NPN transistor to a common ground, and through a second resistor to the collector of said transistor, and through a third resistor and the anode and cathode in that order of an SCR to common ground, the base of said transistor also connected to said source of negative pulses, the collector of said transistor also connected through a fourth resistor to common ground and through the anode and cathode of a first diode and a fifth resistor to common ground, a capacitor being in parallel with said fifth resistor, the cathode of said first diode connected to one terminal of a breakdown diode the other terminal of said breakdown diode connected to the gate of said SCR and through a sixth resistor to common ground, and a second diode cathode connected 10 to the anode of said SCR, whereby a ready conducting path is provided between the anode of said second diode and common ground when said source of negative pulses has provided an uninterrupted series of negative pulses to said disabling circuit for a predetermined time.

11. For energizing a direct current actuated electromechanical device having a winding from a source of alternating current power, a circuit comprising in series combination said source, a rectifier, said winding and a resistance, and a capacitor in parallel connection across said winding and said resistance, said resistance having a value suflicient to limit the current flow in said winding to that requisite to actuate said device, wherein a failure of any one of the resistance, capacitor or rectifier will result in non-actuation of said device.

References Cited UNITED STATES PATENTS 2,675,069 4/1954 Shottenfeld 43766 3,348,104 10/1967 Zielinski et a1. 317- EDWARD G. FAVORS, Primary Examiner US. Cl. X.R. 

